Claims:WE CLAIM:
1. A prepreg and sheet/film composition comprising of ferrites, fibers, a binder, one or more composite surfaces, an adhesive composition and a protective surface coating.
2. The prepreg and sheet/film composition in claim 1 wherein ferrite is comprised of ferrite, ferrite blends or doped ferrite or a mixture of ferrite, ferrite blends and doped ferrite.
3. The prepreg and sheet/film composition in claim 1 wherein the thickness of films is in the range of 0.1 mm to 10 mm .
4. The prepreg and sheet/film composition in claim 1 wherein binder comprises 1 to 95 parts of the sheet/film.
5. The prepreg and sheet/film composition in claim 1 wherein ferrite, doped ferrite and ferrite blends comprises 1 to 95 parts of the sheets/film.
6. The prepreg and sheet/film composition in claim 1 wherein binders is one of polyurethanes, polychloroprene, PPS, PES, Epoxy, Polyimide, Cyanate ester, PEEK based formulations with additives , pigments, catalyst, hardeners.
7. The prepreg and sheet/film composition in claim 1 wherein ferrite is doped with nanoparticles, metal particles.
8. Prepreg and sheets/film compositions in claim 1 wherein nanoparticles comprises 0.001 to 5% of the sheets/films.
9. The prepreg and sheet/film compositions in claim 1 wherein nanoparticles is one of graphene, CNT or nano clays.
10. The prepreg and sheet/film compositions in claim 1 wherein fabric is woven, nonwoven or knitted and made of carbon, glass, aramid polyamide or hybrid fabrics.
11. The prepreg and sheet/film compositions in claim 1 wherein steel , nickel copper, graphite or carbon conducting fibers is added to the fabric.
Dated this 29th day of January 2020

Shalini Sitaraman- Agent for the Applicant
Phone: 8600126625
IN-PA-1795
, Description:

FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of invention:
PREPREGS AND FILM/SHEET COMPOSITION

Applicant
The Bhor Chemicals & Plastics Pvt. Ltd.
Shivsagar Estate, 8th Floor, Block 'A',Dr, Annie Besant Road, Worli, Mumbai - 400 018
Inventor
Dr Milind Mukund Khandwe
The Bhor Chemicals & Plastics Pvt. Ltd.
Shivsagar Estate, 8th Floor, Block 'A',Dr, Annie Besant Road, Worli, Mumbai - 400 018
The following specification describes the invention and the manner in which it is to be performed

CROSS-REFERENCE TO RELATED PPLICATIONS AND PRIORITY
[001] The present application does not claim priority from any patent application.

TECHNICAL FIELD
[002] The present disclosure in general relates to the field of material science. More particularly, the present invention relates to sheets ,film or viscous materials which can be applied over surface of an aircrafts, helicopter, UAV, ships, submarines and other ground based objects capable of radar cross section reduction (RCS) and shielding radar signature of objects.
BACKGROUND
[003] There are numerous camouflaging techniques-based on colour, nets, shapes and designs. These has deceivability in UV visible NIR, IR and Radar range, majority of these application falls under counter surveillance of passive or non-moving objects. However, the flying or moving objects require highest level of shielding when in operation with an objective of not disturbing operational and aerodynamic/ergonomic requirements.

[004] The majority of objective of covertness in the cited examples are achieved through shapes. But certain areas where shapes cannot be changed (as per aerodynamic or ergonomic requirements) remain vulnerable to detections.

[005] To protect such vulnerable area surface application of radar absorbing or scattering materials are the solution which are available in intractable powdery or solid forms and are efficiently functional in their morphological state.

[006] A major disadvantage of such powdery material is intractable properties, as they are available in few microns to nano scale particle size and cannot be processed using conventional coating or paint manufacturing techniques keeping the functional morphology intact. The standard processing techniques of milling, grinding alters functional properties of radar absorptions or scattering.

[007] There are many patents covering counter surveillance and covert material and their applications in different ranges of electromagnetic spectrum. US2001/0044489A1 describe about coatings containing low emissivity spheres in silicone resins limited to camouflaging in 3-50 µm range, which restricts it’s usage in IR range of electromagnetic spectrum.

[008] US2003/0051634A1 describes flaky pigments coated with semi-transparent film which can remain functional only in flake form, which indicates that alteration in the surface area due to mechanical and thermal stresses of ordinary formulating equipment like mills, blenders, sigma mixers, etc will change chromaticity or response to electromagnetic radiation. This is a universally applicable concept in most of the functional materials where the properties are dependent on surface geometry or morphology of the particles.

[009] US2007/0251420A1 describes about powder coating formulations behaves as powdery sprayable material under charged environments and can only be applied to electrically conducting surfaces. This type of processing requires high amount of binders and highest particle size reduction which are not desired for effective RCS reduction.

[0010] Russian patent RU2016126502A talks about multilayer arrangement of flat particles on transparent dielectric substance which is practically not possible to achieve in industrial environments and has limited application in to IR range.

[0011] US patent 4606848 describes radar attenuations using paints loaded with thin conducting fibers of carbon, steel, graphite, into standard camouflaging paints where the directionality issue of RCS as well as ease of application of paint containing fibers will be practical difficulties.
[0012] US patent 5348789 describes camouflage net with functional polyester fiber however it has limited usage to put on an object when it is not moving and hence cannot be used in flying aircrafts, UAVs .

[0013] WO2009/017520A3 describe camouflage net comprising conductive fabric which has limited function in 6-8 GHz range that falls between S-band radars and X-band radars.

[0014] EP2766689A2 describes multispectral camouflage nets suitable for stationary objects with limited camouflage in radar range.

[0015] US6613420B1 describe camouflaging in IR region based on the surface geometry which finds limited usage in aerodynamic objects like aircrafts, UAV’s, etc.

[0016] The drawbacks with the existing technology can be summarized as follows:
On analysing prior art as elucidated above, the materials which can be applied in the form of prepreg or viscous latent curing system-based films on the surface of flying/stationary/moving objects for counter surveillance keeping aerodynamic and ergonomic design intact, remains unresolved. In addition, the ease of processing like composites , at the same time capable of providing RCS of 4-23 dB in 2-300 GHz range is also not found in prior art. The modern air and surface operating vehicular structures are now manufactured predominantly using composite materials. The present inventions entirely differ from the prior art as it brings solutions to RCS reduction by absorption and/or scattering of a flying or moving object and application to the surface using conventional equipment and processes used in composite technology as claimed.

Objectives of the invention:
[0017] In radar technology, surveillance is achieved by converting radio frequency into other form of energy by absorbing materials on other hand the scattering material divert the waves so that, signature of object is reduced. The prior art only suggest paint and fabric-based product which has limited response in radar range or can only be deployed on stationary objects. Therefore, the objective of the present invention is to overcome drawbacks of prior arts. The prepregs either thermosetting or thermoplastic in nature, are common building blocks for manufacturing, aircrafts, ships and modern services vehicles. Principle objective is to make available composite compatible materials with covert functionality inbuilt, at the same time synergistic to conventional manufacturing processes. Another objective of invention is to combine absorption and scattering effects so that it can perform RCS reduction in a broad radar range of 2-300 GHz. Selective formulating of absorption and scattering material brings advancement to current technology.

SUMMARY

[0018] This summary is provided to introduce aspects related to a prepreg and sheet or film in the form of prepreg where fibers based knitted, woven or non-woven web will be used for support, which can have functionalized fibers and can provide mechanical reinforcement to form a stable structural layer after curing or thermoforming. The functional alteration of fiber can be done with radar scattering or absorbing materials. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0019] The web is coated or impregnated with radar absorbing or scattering materials or their combination using elastomeric, thermosetting or thermoplastic polymeric binders. This makes an intermediate product in a film or sheet form or a viscous liquid which will adhered to metallic, non-metallic and FRP composite surfaces. To facilitate adhesion of the sheets or films, a primer or adhesive composition containing radar responsive functional materials is also invented. The sheet and films, after application can be coated with common protective surface coatings which are based on polyurethanes or epoxy. Use of surface coating silanes provide unique compatibility and orientation of radar absorbing or scattering materials.
[0020] The material category used to formulate sheets, adhesives, primers, prepregs are based on polyurethanes, polychloroprene, PPS, PES, Epoxy, Polyimide, cyanate ester, PEEK category of formulated polymeric binders. In the case of thermosetting polymers latent catalyst and hardeners are used.

[0021] The absorbing materials consists of ferrite in different compositions and particulate size used either as such or doped with nanoparticles like Graphene, CNT and nano clays. These are also formulated further with Nickel, steel, Graphite fibers.

[0022] Combination of polymeric binders as described above, formulated with absorbing and scattering materials are processed into sheets, without reinforcements or reinforced with fabrics based on glass, carbon, aramid, polyamide and their blends.

[0023] The sheet or film thus formed are protected with released liners made out of siliconized papers and polyethylene film. When prepreg sheets or films are made with catalysed polyurethanes, epoxy or cyanate ester resins, they are stored at 4 °C TO -18 °C.

BRIEF DESCRIPTION OF DRAWINGS
[0024] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

[0025] Figure 1 illustrates Fabric layers of functional and/or support nature on both the sides. Ferrite/doped ferrite with thermosetting latent cure or thermoplastic binder with or without curing agents.

[0026] Figure 2 illustrates Reinforcing fabric layer for the sheet impregnated with Ferrite/doped ferrite with thermosetting latent cure or thermoplastic binder with or without curing agents.
[0027] Figure 3 illustrates Fabric layer supported on one side and cable of multilayer assembly of sheets, other side being Ferrite/doped ferrite with thermosetting latent cure or thermoplastic binder with or without curing agents.

[0028] Figure 4 illustrates Reference setup for RCS measurements.

DETAILED DESCRIPTION
[0029] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any prepregs and film sheets for radar cross section reduction similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the prepregs and film sheets for radar cross section reduction as claimed are now described. The disclosed embodiments for are merely examples of the disclosure, which may be embodied in various forms.

[0030] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments for prepregs and film sheets for radar cross section reduction.

[0031] However, one of ordinary skill in the art will readily recognize that the present disclosure for prepregs and film sheets for radar cross section reduction is not intended to be limited to the embodiments described, but is to be accorded the widest scope consistent with the principles and features described herein. The present disclosure relates to prepregs and film sheets for radar cross section reduction.

[0032] One embodiment discloses a prepreg and sheet/film composition wherein the sheets/films are composed of ferrite, ferrite blends, doped ferrite, fabric and binders.

[0033] Another embodiment discloses a prepreg and sheet/film composition wherein the thickness of films can be in the range of 0.1 mm to 10mm and the binder comprises 1 to 95 parts of the sheets/film.

[0034] Yet another embodiment discloses a prepreg and sheet/film composition wherein ferrite ,doped ferrite and ferrite blends with conducting materials comprises 1 to 95 parts of the sheets/film and ferrite may be doped with nanoparticles, metal particles.

[0035] One embodiment discloses a prepreg and sheet/film composition wherein binders could be one of polyurethanes, polychloroprene, PPS, PES, Epoxy, Polyimide, Cyanate ester, PEEK based formulations with additives , pigments, catalyst, hardeners.

[0036] Another embodiment discloses a prepreg and sheets/film compositions wherein nanoparticles comprises 0.001 to 5% of the sheets/films. Yet another embodiment discloses a prepreg sheet/film compositions wherein nanoparticles could be one of graphene, CNT or nano clays.

[0037] One embodiment discloses a prepreg and sheet/film compositions wherein fabric could be woven, nonwoven or knitted and made of carbon, glass, aramid polyamide or hybrid fabrics and wherein steel , nickel copper, graphite or carbon conducting fibers may be added to the fabric.

[0038] The ferrites are cubic crystalline material characterized by its spinal structure containing Fe2O3 and at least one other oxide. Nickel ferrite (NF), Zinc ferrite (NZF), Calcium/Barium/Strontium hexaferrite and several other metal ferrites are evaluated and formulated, further Carbonyl and Graphene, CNT, Nano doped ferrites are also used for formulating absorbing/scattering powders.

[0039] Few correct combinations found useful in providing desired RCS when combined with silane surface coatings or silicone surface coating, these materials cannot be subjected to heavy milling and grinding techniques which are common in manufacturing of paints and coatings. Therefore, selected molecular weight distribution based polymeric binders are used. The polyurethanes when used as binders are based on aromatic and aliphatic polyols as well as PEG of different molecular weights. PEEK in the form of dispersion and micronized powders used for making a master batch. Polydimethylsiloxanes and polyfluorosiloxomes, polychloroprene were used alone as binder for ferrites. Nylon 66 and Nylon 11, PES. DEGBA, trifunctional cycloaliphatic tetrafunctional and multifunctional aromatic epoxy resins in combination with latent curing agents are used as beinders. The radar absorbing / scattering functional materials and polymeric binders have been combined using soft mixing techniques, grinding in cryogenic state, use of solvents like MEK, Toluene, Cellusolve and water as dispersing agents. The formulation may contain dispersing agents, wetting agents, catalysts, hardeners of latent nature. Ferrite powders to binder ration were ranging from 1 to 95%. The formulated compounds are applied on fabrics/fibers based reinforcements. Woven fabrics were used where dimensional stability required and object surfaces were plain. Knitted or non-woven were used as per the drape requirements of objects of the surfaces. All the reinforcing fabric materials are based on glass, quartz, carbon, aramid, polyamide, polyester fibers or their combinations.

[0040] The fabrics are also functionalized with graphenes, CNT based nanomaterials to obtain additional RCS, for the same reasons the fabric also woven with metallic fibers like aluminium, steel, copper or nickel. The formulated ferrite, polymeric binders, combination were applied or impregnated into fabric with uniform thickness using a casting, coating or powder scattering machines. Few formulations were developed without the carrier or reinforcing textile web. Thus films of polymeric binder and powder formed, are sufficient to be deployed on a required equipment surface. The surfaces under consideration are mainly outer surface of aircrafts, helicopters, UAVs, ships , underwaterand surface operating vehicles, etc.. Thus the prepreg and sheet/ films can be applied on steel, aluminium alloys, fiber reinforced composites & glass.

[0041] Examples: The invention is illustrated by few examples, the materials among and procedures are given for understanding the spirit of invention.

[0042] Example 1 – Hydroxyl terminated a polysiloxane based polyols are dispersed with ferrite powder so that, the individual particles get coated. In few cases fluorosilicone polymers are also used. The process of coating continued over a period of 2 hours to several days. (30 days) the siloxane coated powder was dispersed into standard polyols, PPG 400 to PPG 2000. Desmophenes or desothenes are also used. The composition is mixed with end caped Isocynates and impregnated into 200 GSM Glass fabric under 6 bar pressure. sheets of 1-2 mm thus form are protected with siliconized paper and stored at 4 ?C.

[0043] Example 2: A combination of Barium ferrite powder doped with graphenes and dispersed with milled carbon fibers was coated with silane composition. Typical silane composition which are known for self assembled mono layer or micro contact printing, for example, Octadecylmethyl(3-trimethoxy-silyl-propyl) or n-methyl amino propyl tri-methoxy silane and similar derivatives. These surface treated powder composition were further dispersed into epoxy resins with latent catalysts, polychloroprenes, rubber or PEEK dispersions. These compositions were spread into films and sheets and protected with siliconized papers or polyethylene films.

[0044] Example 3: the sheets/ films thus formed can be activated at 100-180 C under pressure on desired surfaces or co-cured during composite formation. A typical carbon prepreg based fuselage of an aircraft prepared in situ moulding. To bring adhesion to surface an epoxy primer was used, and the final surface was protected with HSCA8000 polyurethane top coat.

[0045] Example4: Several sheets of composites as described in examples 1&2, where casted in thickness range of 0.25-6 mm and dimension of 300 mm X 300 mm., in many cases multiple layers are pressed under 1-6 bar pressure and 40-150 C Temperature. The cross section of few typical sheets are shown in drawing 1-3. To measure the radar cross section reduction, the sheets were placed between horn and receiver antenna assembly, shown in drawing no. 4. The radar attenuation (RCS) of 4-23 dB is observed in different cases for example in S-band, C- band X-band, Ku – band K band Ka -band etc.

[0046] With a simple indoor setup and placing the transmitter horn and receiver antennas in the scheme as shown in Figure 4, it is possible to measure the RCS of targets in different frequency ranges by changing frequency and horn and antenna types. This is used in laboratory evaluation prior to field tests.